Niccolo Machiavelli, when not engaged in scheming and political conniving, had an amateur's interest in the science of hydrology. He knew that rural and urban flooding often arise from different causes.
The low gradient of many rural landscapes makes for slow and ponderous rivers with a poor carrying capacity, and when there is an excess of rainfall they sometimes cannot cope and overflow their banks to inundate the countryside around. Urban flooding, on the other hand, may sometimes be an engineering problem; locally intensive rainfall may be beyond the design capacity of the sewered drainage system.
There are also two schools of thought as to how we ought to deal with flooding problems. Machiavelli, as one might expect from his reputation, favoured the proactive approach, and describes it in some detail in The Prince. He writes of "one of those raging rivers, which when in flood overflows the plains, sweeping away trees and buildings, bearing away the soil from place to place".
"Everything flies before it," he continues, "and all yield to its violence, without being able in any way to withstand it. And yet, though its nature be such, it does not follow therefore that men, when the weather becomes fair, shall not make provision, both with defences and barriers, in such a manner that, rising again, the waters may pass away by canal, and their force be neither so unrestrained nor so dangerous."
And, of course, it can be done. The problems are often caused by the inability of the waterway to cope with an unusually large amount of water, and there are ways of removing the danger. The channel available to the river can be enlarged; or alternative routes can be provided at critical points for the excess water - like underground pipes or surface canals; or sometimes it may be feasible to build embankments to hold back the floodwaters from vulnerable areas.
Others, however, advocate a more laissez-faire approach. They feel that rivers are meant to flood, that they must have room to move, and that we ought to plan our lives, our living quarters and our agricultural activities so that we keep out of their way. As one proponent puts it, "River flood is not in the normal course of things a natural disaster. Where man for his own good reasons, or through his own shortsightedness, has chosen to construct works by the side of a river, then indeed these manmade worlds may be disastrously damaged by a flood.